Decoding the Mystery of QR Codes

5 min readJun 10, 2024

Introduction

QR is short for Quick Response, these codes are found everywhere — from product packaging to payment systems. They offer a fast and efficient way to store and share information. This blog includes the technical workings of QR codes, including their creation, encryption, decryption, and usage.

What is a QR Code?

A QR code is a two-dimensional barcode that can store many different data types, such as URLs, text, and binary data. Unlike normal barcodes that store information in a small rectangular series of lines with different widths, QR codes store data in a square shape, allowing for much larger amounts of data to be encoded.

Structure of a QR Code

A QR code has several black and white squares arranged in a unique order on a square grid with a white background. A few of the key structural components of QR codes are:

Finder Patterns: Located at three corners, these help the scanner detect the code’s position, size, and orientation.
Alignment Patterns: Ensure the code can be read correctly even if it is distorted or skewed.
Timing Patterns: Help determine the width of the smallest black or white square(module).
Format Information: Contains error correction level and mask pattern information.
Data and Error Correction Keys: Store the actual data and error correction data.
Quiet Zone: A margin space around the QR code, is essential for proper scanning.

How QR Codes are Generated

Creating a QR code involves encoding data into a grid of black and white squares. This is the detailed process:

Data Encoding: The data is converted into a bit stream using one of these encoding modes; numeric, alphanumeric, binary, or kanji.
Error Correction: QR codes use Reed-Solomon error correction. Depending on the chosen error correction level (L, M, Q, H), the QR code can recover from a certain percentage of damage.
Structure Final Message: The encoded data is divided into codewords (8-bit units), with error correction code words added to the data codewords.
Module Placement: The final bit stream is placed into the QR code matrix, including finder patterns, alignment patterns, and timing patterns.
Masking: A mask pattern is applied to make sure that the QR code is easy to read. The mask changes some bits in a predictable way to avoid patterns that can confuse the scanner.

How QR Codes are Decrypted

Decrypting a QR code is essentially scanning it for a purpose. Scanning a QR code involves these steps:

Image Capture: The QR code is captured using a camera.
Localization: The scanner identifies the finder patterns to locate the QR code within the image.
Grid Sampling: The image is sampled to extract the grid of black and white modules.
Data Extraction: The encoded data and error correction codewords are extracted from the sampled grid.
Error Correction: Using the error correction codewords, the scanner corrects any errors in the data.
Data Decoding: The corrected data is then decoded back into its original form.

Example of QR Code Decryption

Let’s take a QR code encoding the URL “https://example.com". The decryption process would involve:

The URL is converted into a binary format.
Error correction codewords are added.
The data and error correction codewords are placed into the QR code matrix.
A mask pattern is applied.

When scanned, the process is reversed:

The QR code image is captured.
Finder patterns are detected.
The grid is extracted.
Data and error correction codewords are extracted.
Errors are corrected.
The original URL is retrieved.

Practical Applications

QR codes can be used in the following ways:

Marketing: Directing users to websites or promotional content.
Payments: Facilitating quick and secure transactions.
Authentication: Verifying product authenticity.
Information Sharing: Providing detailed information about products or services.

Ensuring Uniqueness and Proper Routing of QR Codes

Each QR code is unique due to its encoded data, which makes it different from others. Here’s how the uniqueness and proper routing of QR codes is ensured:

Data Variability: The encoded data within each QR code is unique, such as a distinct URL, text, or binary data. This variability makes sure that each QR code is unique.
Error Correction: The error correction codes in each QR code not only ensure data integrity but also contribute to its uniqueness by making sure that the correct information can be recovered even if part of the code is damaged.
Dynamic QR Codes: These codes can be updated and managed through a central server. When a dynamic QR code is scanned, the server routes the request to the current data associated with that QR code. This ensures that even if the data changes, the QR code remains unique and still works.
Centralized Management Platforms: Platforms that generate and manage QR codes often provide unique identifiers and tracking mechanisms. These platforms ensure that each QR code directs to the correct resource and can track scans and usage.
Secure Generation Protocols: Reputable QR code generation services follow secure protocols to prevent duplication and ensure that each generated code is unique.
Regular Audits and Monitoring: Organizations that rely heavily on QR codes, especially for payments or authentication, often use regular audits and monitoring systems to detect abnormalities and misuse.

Registration of QR Codes

QR codes themselves don’t need to be registered, but, the content they redirect to generally does. For example, URLs encoded in QR codes should have a registered and managed domain. Companies may register their QR codes with relevant industry sections or standard organizations to make sure that they are secure. This applies in the context of proprietary QR codes which are codes that are used for payments or product verification.

Conclusion

QR codes are a vital tool for encoding and sharing information quickly and efficiently. Understanding their technical workings, from data encoding and error correction to masking and decoding, shows that QR codes are more than just black and white squares. Whether used for marketing, payments, or authentication, QR codes are a huge part of today’s digital world.